[426] The second-generation jet
transports are considered to be those [427]
which first flew in prototype form in the 1960's. The following 11 aircraft
constitute the second-generation jet transports:

Country

Manufacturer

Model

First flight a

Engines

United States

Boeing

727

1963

3

United States

McDonnell Douglas

DC-9

1965

2

United States

Boeing

737

1967

2

United Kingdom

British Aircraft Corporation

1-11

1963

2

United Kingdom

Hawker Siddley

Trident

1962

3

United Kingdom

British Aircraft Corporation

VC-10

1962

4

Netherlands

Fokker

F-28

1967

2

U.S.S.R.

Tupolev

Tu-134

1964

2

U.S.S.R.

Tupolev

Tu-154

1968

3

U.S.S.R.

Ilyushin

Il-62

1963

4

U.S.S.R.

Yakolev

Yak-40

1966

3

First flight dates for prototype of first version

Most of the aircraft listed are representative of about
the same level of technology and have no large state-of-the-art advances over
the first-generation jet transports previously discussed. All the aircraft
are equipped with turbofan engines of relatively low bypass ratio that are
of about the same level of technical sophistication as the fan engines that
powered the first - generation transports. Basically, with a few evolutionary
refinements, the second - generation aircraft represent an application of
the technology developed in the first - generation aircraft to transports
specifically tailored to various types of airline route structures and payload
requirements. All the aircraft, except the Boeing 737, employ aft-fuselage-mounted
engines in either two - , three - , or four-engine configurations. Four of
the aircraft are briefly described in the following paragraphs; they are the
three-engine Boeing 727, the twin-engine McDonnell Douglas DC-9, the twin-engine
Boeing 737, and the four-engine British Aircraft Corporation VC-10.

Boeing 727

By any standard, the three-engine Boeing 727 must be
considered the most successful jet transport aircraft yet produced. The prototype
first flew in 1963, and the type was introduced into service by Eastern Airlines
in early 1964. Total orders to mid-1982 numbered 1825, with [428] the aircraft being produced
at the rate of 2 per month1 . The 727 is operated all over the world by some 85 airlines;
It is rarely possible to - visit a domestic airport served by a scheduled
airline without seeing a Boeing 727 during the course of a day. The 727 is
popular with the airlines primarily because it can be operated profitably
over range segmerits of various lengths and passenger-load requirements, and
its relatively short field capability permits operation from a large number
of airports too small to accommodate 707 class aircraft. Many studies were
made over the years in an effort to find a replacement for the ubiquitous
Douglas DC-3; though with different range and payload characteristics, and
with different field length and cruising speed capabilities, the 727 may be
considered as the modern-day counterpart of the DC-3 that first appeared in
1935.

The aircraft was first produced as the 727-100, and
a later stretched version designated the 727-200 was introduced. Of the 1825
aircraft so far ordered, over 1300 have been for the 727-200, which is the
only version now in production. The aircraft is produced in both passenger
and convertible cargo-passenger configurations. A 727-200 in American Airlines
markings is shown in figure 13.12, and the characteristics of this version
of the aircraft are given in table VII.

The choice of three engines for the 727 was dictated
by a compromise between cost and airport performance. For operation on hot
days from airports located at high altitudes, the three-engine arrangement...

Figure 13.12 - Boeing 727-200 medium-range airliner.
[mfr]

[429] ....offered significantly
better takeoff and climb performance withengine out than was practical for an efficient twin-engine design,
butat a great
deal lower cost than for a four-engine aircraft. Aninterestingdiscussion of this trade-off,
as well as other aspects of the design anddevelopment of the 727, is contained in reference 145.

The most distinguishing recognition feature of the 727
is probably the mounting of the three engines, which are located at the aft
end of the fuselage. The inlet for the center engine is on top of the fuselage
ahead of the vertical tail. The engine itself, however, is located in the
fuselage in the same horizontal plane as the two outboard engines and exhausts
through the tail end of the fuselage. Placement of the three engines in this
way simplifies maintenance and servicing and allows a high degree of commonality
in ground-support equipment. This arrangement, however, necessitates the use
of an S-shaped duct to deliver air from the upper-fuselage-mounted inlet to
the front face of the center engine. The design of inlet and duct for the
center engine requires careful attention if unacceptable internal aerodynamic
losses are to be avoided. The advantages and disadvantages of the aft-fuselage-engine
location have been discussed in connection with the twin-engine Caravelle
and apply equally well to a three-engine design like the 727. Arrangement
of nacelles and exhaust nozzles are shown in the rear view of a 727-100 presented
in figure 13.13. Also note the rear-loading stair. Flight tests of a rear-fuselage-mounted
engine were made on the Boeing 367-80 to prove acceptable engine operation
with the wing in a stalled condition. This test arrangement is shown in figure
13.14.

Power for the 727-200 is supplied by Pratt & Whitney
JT813-17 engines of 16 000 pounds thrust each. These engines, which have a
bypass ratio of 1.06, have probably been used to power more jet transport
aircraft than any other engine.

The 727-200 is seen from figure 13.12 to be a low-wing
design; according to the data given in table VII, the wing planform geometry is similar to that of the 707. The
engine arrangement results in a horizontal tail mounted at the tip of the
vertical fin in a T-tail configuration. Some of the advantages and disadvantages
of this arrangement are briefly discussed in chapter 10 as well as in this chapter in connection with the Sud-Aviation
Caravelle. The lateral and longitudinal control surfaces are of the same type
as those employed on the 707. In contrast to the 707, however, all the controls
on the 727 are hydraulically actuated. In order to allow operation from airports
of medium size, the 727 is equipped with very powerful high-lift devices.
The...

[430] Figure 13.13 - Rear view of Boeing 727 airliner. [mfr]

....trailing edge of the wing has triple-slotted flaps
of the type shown schematically in figure 10.25(a) and illustrated in figures
10.26 and 10.27. The leading edge has a slat on the outboard two-thirds of
the span and Krueger flaps on the inboard portion of the wing. With these
high-lift devices, a stalling speed of 121 miles per hour is obtained at the
maximum landing weight of 160 000 pounds. The main landing gear employs two-wheel
bogies instead of the four-wheel type used on the 707. The gear retracts inward
into the wing at the root. The leading - and traling-edge high-lift devices
are shown in the takeoff position in figure 13.15. Also note the large negative
deflection of the horizontal tail and the flame trailing from the tail skid
as it drags along the runway. The dramatic high-angle-of-attack takeoff illustrated
in figure 13.15 was made for test purposes and is not typical of normal operating
practice.

The Boeing 727-200 has a gross weight of 210 000 pounds
and in full touristconfiguration
can accommodate 189 passengers in a 6-abreast arrangement. The upper fuselage
diameter of the aircraft is the....

....same as that of the 707 and the shorter range Boeing
737. Thus, to the passenger, all three aircraft appear to have the same cabin
size except for length. The 727-200 is capable of a maximum range of 3738
miles with full fuel tanks; with maximum payload, it has a range of 3335 miles.
The cruising speeds of the aircraft are comparable to those of the 707 and
the DC-8.

[432] McDonnell Douglas DC-9

The twin-engine McDonnell Douglas DC-9, in its many
versions, generally has a smaller passenger capacity, shorter range, and shorter
field length capability than the Boeing 727. It has been produced In six major
versions and is now in operation on airlines all over the world. The six versions
now in operation vary in (1) passenger capacity from 90 to 172, (2) length
from 104 to 147 feet, and (3) gross weight from 80 000 to 148 000 pounds.
Perhaps more than any other aircraft type, the DC-9 represents an entire family
of aircraft. The prototype of the DC-9 first flew in February 1965, and nearly
1100 examples have been produced to date. The type is still in production
at the rate of four or five per month, and it seems destined to roll off the
production lines for several more years to come.

The DC-9-30, one of the most numerous versions of' the
aircraft, is illustrated in figure 13.16 in the Royal Dutch Airlines livery,
and some of the characteristics of this aircraft are presented in table VII. Basic configuration of the aircraft is similar to that of the
Caravelle in that the two engines are mounted in the aft-fuselage position.
The T-tail arrangement
employed by the DC-9, however, is different from that of the Caravelle. The
engines that power the aircraft are the same basic Pratt & Whitney JT81)
turbofans as are employed on the Boeing 727. For this particular version of
the DC-9-30, the two engines have 15 500 pounds of thrust each.

The sweptback wing of the DC-9 has a somewhat smaller
sweep angle than that of the 727, and the cruising speeds given in table VII...

[433]....for the aircraft are correspondingly
lower than those of the 727. Aspointed out in the discussion of the Caravelle, the lower cruising
speed of the DC-9 results from tailoring the characteristics of the aircraft
to relatively short range segments and small airports for which it wasintended. The high-lift system on most versions
of the DC-9 consistsof
trailing-edge double-slotted flaps and leading-edge slats (the DC-910 had
no slats). The lateral control system utilizes inboard and outboard ailerons,
with the outboard ailerons being used only at low speeds as in the DC-8. Speed
brakes are mounted on the upper surface of the wing. With the exception of
the elevators, all the control surfaces are hydraulically actuated. As in
the DC-8, the elevators of the DC-9 are manually controlled through aerodynamic
servotabs.

The gross weight of the DC-9-30 is 109 000 pounds, which
is about half that of the 727-200, and the 115 tourist-class passengers are
seated in a 5-abreast configuration. The higher thrust loading and lower wing
loading of the DC-9, as compared with the 727, result in a much lower takeoff
field length for the Douglas aircraft; the landing field lengths for the two
aircraft, however, are about the same. The range at maximum payload for the
DC-9-30 is 1812 miles, which is about half that of the Boeing 727. Clearly,
the DC-9 and 727 are intended for different types of airline-route structures
and passenger-load requirements. Both highly successful aircraft complement
each other in airline operation, and both seem destined to fly on together
for many years.

Boeing 737

The twin-engine Boeing 737 was developed as a direct
competitor of the McDonnell Douglas DC-9 but did not fly until about 2 years
after the latter's introduction. The 737 has been produced in two versions,
the 737-100 and the 737-200. Except for 30 units, all the aircraft produced
have been the 737-200 version, which is a stretched, higher capacity, and
heavier aircraft than the 737-100. The total number of orders for the 737
was 978 by mid-1982, and the type is currently being manufactured at the rate
of 8 per month (ref. 150).

A Boeing 737-200 in United Airlines' markings is shown
in figure 13.17, and some of the characteristics of the aircraft are given
in table VII . The two engines are mounted under the wings in a manner similar
to that of the 707. The proximity of the engine nacelles to the under surface
of the wing highlights the problem, previously mentioned, incurred by the
underwing engine location as the size of the aircraft is reduced. The desire
to avoid a high-mounted horizontal tail, and its...

....possible stability problems, apparently was largely
responsible for the choice of this engine location instead of the aft-fuselage-mounted
arrangement. As figure 13.17 shows, the horizontal tail is located on the
fuselage below the root of the vertical tail. The 737 uses basically the same
Pratt & Whitney engines as those employed on the Boeing 727 and the McDonnell
Douglas DC-9.

The 737 fuselage appears short and stubby, due to its
large upper-fuselage diameter, which is the same as for the 707 and the 727,
and its short length, which is less than for the 707 or the 727. The higher
fineness ratio fuselage and greater length of the DC-9 results from the use
of a five-abreast seating arrangement and consequent smaller fuselage diameter.
The short fuselage length of the 737 along with the wide lateral separation
of the underwing-mounted engines result in the large vertical tall on the
aircraft.

The geometry of the 737 wing is very similar to that
of the DC-9 as is shown by the data in table
VII. The high-lift and control systems of the
737 are like those described for the 727.

An examination of' the data in table
VII for the 737-200 and the DC-9-30 shows a
close similarity in the size, weight, and performance of the two aircraft.
This similarity Would be expected since they were designed for similar operations.
The major difference in performance of the two aircraft is the longer range
of' the 737 with full fuel tanks.

[435] A major new derivative of
the Boeing 737 is under development and scheduled for initial deliveries late
in 1984. Designated the 737-300, the new aircraft will be a stretched, heavier
variant of the 737-200 powered with the GE Snecma CFM turbofan engines of
20 000 pounds thrust and bypass ratio of 6.0. Lower seat-per-mile costs and
reduced noise are among the advantage offered by the improved aircraft.

British Aircraft Corporation VC-10

Two long-range, four-engine, heavy jet transports were
developed in the 1960's. These were the British VC-10 developed by VickersArmstrongs, which later was absorbed into the
British Aircraft Corporation, and the Soviet Ilyushin Il-62. The two aircraft
closely resemble each other in configuration and employ an engine arrangement
different from any existing four-engine jet transport. On each aircraft, the
four engines are mounted at the aft end of the fuselage, two on either side,
in a four-engine adaptation of the twin aft-engine configuration pioneered
by the Caravelle. Both aircraft weigh over 300 000 pounds, and both were designed
for long-range operation.

The VC-10 was developed in response to a requirement
of the overseas division of British Airways, formerly the British Overseas
Airways Corporation (BOAC), for use on its long-range routes to Africa, India,
and Australia. First flight took place in June 1962, and the type entered
service with BOAC in April 1964. Production of the aircraft was terminated
in 1974 after 54 units were manufactured.

The VC-10 is shown in figure 13.18, and some of the
characteristics of the aircraft are given in table
VII. The four aft-mounted engines are, of course,
the most distinctive feature of the configuration. The power is supplied by
Rolls-Royce Conway turbofan engines of 21 000 pounds thrust each. These engines
have a bypass ratio of 0.6 and employ a four-stage front-mounted fan.

Like all aircraft that employ the aft-mounted engine
arrangement, the wing of the VC-10 appears quite clean and uncluttered. The
sweepback angle is 32.5% and the aspect ratio is 6.9. Although the sweep angle
is slightly less than that of the Boeing 707, the wing-plan-form geometry
employed on the two aircraft is nearly the same. The high-lift system consists
of trailing-edge Fowler flaps, which are similar to the double-slotted flap
shown in figure 10.25(b) with the small middle element removed, and leading-edge
slats. Three leading-edge fences are employed on each wing, as can be seen
in figure 13.18. Lateral control is provided by a combination of ailerons
and spoilers. The....

....spoilers are also used as air brakes and can be
seen deployed as such in figure 13.18. All control surfaces are hydraulically
actuated.

A comparison of the performance data of the VIC-10 and
the Boeing 707-320B given in table VII indicates that the maximum payload and corresponding range are
significantly less than those of' the Boeing 707-320B. The cost-economical
cruising speeds of the two aircraft are also about the same; however, the
maximum cruising speed of' the 707 is somewhat higher than that of the VC-10.
Many of the airports served by British Airways are located in tropical or
subtropical areas characterized by high temperatures. Such temperatures increase
the ground speed required for takeoff and reduce the maximum thrust produced
by the engines. The VC-10 was accordingly designed to cope with these difficult
takeoff conditions that, in some cases, were aggravated by airport elevations
considerably above sea level. As a consequence, the takeoff field length for
"standard day" conditions given in table
VII is about 2000 feet shorter for the VC-10
than for the 707.

The VC-10 is no longer in airline service, but a few
are in the Royal Air Force inventory. The economics of' the aircraft apparently
could not compete successfully with those of the Boeing 707 and McDonnellDouglas DC-8; hence, the VC-10 enjoyed a relatively
limited production run. The Soviet 11-62, counterpart of the VC-10, is stillin production and is widely used on Aeroflot's
long-range routes. According to reference 150, about 190 of these aircraft have been constructed.

1 The last Boeing 727, a
cargo version, will be delivered in August 1984; the total number of 727 aircraft
produced will be 1832.